Question

A book of weight $20$ $N$ is pressed between two hands and each hand exerts a force of $40$ $N$. If the book just starts to slide down, then the coefficient of friction is

• A. $0.25$
• B. $0.2$
• C. $0.5$
• D. $0.1$

Answer 1

The correct option is A $0.25$

We know:
frictional force $=\mu$ x normal force
Now,
The book is pressed by two $40$ $N$ force acting normal, and the book tends to slide down,
Thus, frictional force $=2\times \mu N$
$\therefore 2\times 40\mu =20\Rightarrow \mu =0.25$